Pressure control valves are primarily used to regulate fluid pressure applied to a downstream fluid-operated device. Proportional pressure control valves regulate fluid pressure proportional to an electric current supplied to an associated solenoid. Typically, pressure control valves include a high pressure port in communication with a supply passage, a low pressure port in communication with a tank, and a control port which delivers fluid under a pre-determined pressure to a fluid-operated device. The valve further includes a sliding spool, biased by a spring, and configured to open and close the various fluid passages. The spool assumes a position when the pressure at the control port and the spring force are balanced with a driving force which depends on a current level used to energize the solenoid.
Flow forces are natural phenomena in proportional pressure control valves. Flow forces, also referred to as Bernoulli's forces, result from the localized pressure drop in the small opening between the metering spool and the valve body. More specifically, as the fluid passes through the restriction in a fluid path, the velocity of the fluid increases. In the high velocity flow, the kinetic energy increases at the expense of the pressure energy, reducing the pressure adjacent the small opening. The localized pressure drop is attributed to inducing a pressure gradient across the body of the metering spool, and generates a flow force acting on the spool in the axial direction. The flow force tends to close the valve, thereby reducing the overall performance of the valve.
One method to control the flow forces was proposed in U.S. Pat. No. 6,655,653 B2 (“the '653 patent”) issued to Walsh on Dec. 2, 2003. The '653 patent describes a valve assembly including a valve body defining first and second flow passages and a valve axially movable in the valve body to control fluid flow therebetween. The valve includes first and second control edges spaced axially and radially such that the valve includes a radially extending surface between the first and second control edges. First and second restrictions are thereby formed between the first and second control edges and the valve body. The first and second restrictions form an intermediate pressure region such that when the first and second flow passages are at different fluid pressures with the fluid flowing past the valve, the intermediate pressure regions act on the radially extending surface of the valve to cancel, or neutralizing the flow forces.
Although the valve assembly described in the '653 patent may counteract the flow forces tending to close the valve, the valve assembly described in the '653 patent does not allow for bi-directional flow. Furthermore, the valve assembly proposed may be more difficult to manufacture.
The valve assembly of the present disclosure is directed to improvements in the existing technology.